Investigating the Effect of Porosity on Corrosion Resistance and Hardness of WC-Co Coatings on Metal Substrates

Abstract

The effect of porosity on the hardness and corrosion resistance of WC‐17Co coatings on metal substrates was studied. Coatings of about 200±0.6μm thick were successfully deposited by HVOF onto four metal substrates: brass, 304L stainless steel, super‐invar and an aluminium 2xxx alloy. Electrochemical measurement techniques, including open circuit potential (OCP) and potentiodynamic polarisation, were used to evaluate the corrosion behaviour of the coatings in aerated 3.5% NaCl solution. The microstructures of the coatings were studied before and after the corrosion tests by scanning electron microscopy with EDX, and Vickers hardness measurements were undertaken. The porosities of the coatings were measured on the SEM‐BSE images (5000x) of the cross‐sections by dot counting with a grid. The results indicated a strong correlation between porosity and corrosion rate, as well as hardness of the WC‐17Co coatings.